1. Field of the Invention
The present invention relates to a heat-dissipating fan and, more particularly, to a miniature heat-dissipating fan that includes a stator having a reduced axial thickness.
2. Description of the Related Art
A conventional heat-dissipating fan is described in China Patent Publication No. 101060766 (with Application No. 200610072272.8) entitled “SMALL HEAT-DISSIPATING DEVICE”. Referring to FIGS. 1 and 2, the conventional heat-dissipating fan 8 includes a casing 81 defining a compartment 811 and a lid 82 mounted on a top of the casing 81. A circuit board 83 and coils 84 are mounted to a base 812 delimiting a bottom of the compartment 811. An axial tube 813 extends from a center portion of the base 812, with an impeller rotor 86 being coupled rotatably in the compartment 811 by the axial tube 813. Furthermore, at least two positioning members 85 are provided on the base 812 and located outside the axial tube 813. As shown in FIG. 2, a magnet 861 and a metal ring 862 are fixed to a bottom surface of the impeller rotor 86, with the metal ring 862 being sandwiched between the impeller rotor 86 and the magnet 861. In use, the coils 84 are provided with an electric current to generate flux linkage between the coils 84 and the magnet 861, such that the impeller rotor 86 is driven by the excited coils 84 to rotate. Hence, the conventional heat-dissipating fan 8 can be mounted to an electronic device or electronic apparatus and dissipate heat generated by said electronic device or electronic apparatus.
Nevertheless, said conventional heat-dissipating fan 8 has several drawbacks as follows:
First, the metal ring 862 provides a leakage flux absorbing effect during rotation of the impeller rotor 86 that is driven by alternating magnetic fields generated by the coils 84. However, the metal ring 862 only can prevent an occurrence of magnetic flux leakage above the coils 84 and the magnet 861. Thus, magnetic flux that is generated by the coils 84 and doesn't react with the magnet 861 results in magnetic flux leakage under the coils 84 to cause electromagnetic interference (EMI), so that functions of the electronic device or electronic apparatus may easily be affected.
Second, the current trend of research and development in electronic products is miniaturization. However, the circuit board 83 and the coils 84 both have fixed axial thicknesses, which lead to a difficulty in reducing the entire axial thickness of the conventional heat-dissipating fan 8. As a result, minimizing dimensions of the conventional heat-dissipating fan 8 is not feasible, so that it is hard to apply the conventional heat-dissipating fan 8 to a miniature electronic device or electronic apparatus.
Another conventional heat-dissipating fan, Taiwan Patent Issue No. 1293106 entitled “THIN TYPE FAN”, is illustrated in FIGS. 3 and 4. The conventional heat-dissipating fan 9 includes a base plate 91 having an axial hole 911 and a plurality of stator coils 912, a flat-type impeller 92 having a series of bent vanes 921, a magnet sheet 93 attached to a bottom of the flat-type impeller 92, and a shaft member 94. One end of the shaft member 94 extends into the axial hole 911 of the base plate 91, and the other end of the shaft member 94 is fixed to the flat-type impeller 92. Therefore, the conventional heat-dissipating fan 9 can be mounted to an electronic device or electronic apparatus to provide a heat dissipating effect.
However, owing to the fixed axial thicknesses of the base plate 91 and the stator coils 912 of the conventional heat-dissipating fan 9, it is difficult to reduce the entire axial thickness of the conventional heat-dissipating fan 9, too. Also, a difficulty of minimizing dimensions of the conventional heat-dissipating fan 9 is caused, and, thereby, the conventional heat-dissipating fan 9 is hard to be mounted to a miniature electronic device or electronic apparatus. Hence, there is a need for an improvement over the conventional heat-dissipating fan.